Tantalum doped nickel-zinc ferrite



Sept. 26, 1967 TSUNEO AKASHI ET AL 3,344,072

TANTALUM DOPED NICKEL-ZINC FERRITE Filed- Feb. 25. 1964 l I 2Sheets-Sheet l a 7:42 d, (Maz 'Zj Sept. 26, 1967 TSUNEO-AKASH| ET ALTANTALUMv DOPED NICKEL-ZINC FERRITE Filed Feb. 25. 1964 @yx/ff 2Sheets-Sheet 2 United States Patent C) m l 3,344,072 TANTALUM IBPEDNiCKEL-ZNC FERRITE Tsuneo Akaslii and Hideo Takamizawa, Tokyo, Japan,

assignors to Nippon Electric Company Limited, Minatoku, Tokyo, JapanFiled Feb. 25, 1964, Ser. No. 347,176 Claims priority, applicationJapan, Feb. 28, 1963, .3S/10,780 4 Claims. (Cl. 252-626) The presentinvention relates to magnetic oxide materials, and particularly tonickel-zinc ferrites which may be used, for example, in communicationsdevices operating at high frequencies.

It is known that nickel-zinc ferrites can be utilized in diverse fieldsas low-loss magnetic materials suitable for high frequency applications.Nevertheless, the application of nickel-Zinc ferrites in the design andoperati-on of coils and transformers for communications use has beenfound unsatisfactory, primarily because known nickel-Zinc ferritespossess relatively large positive temperature coefficients of initialpermeability.

The principal object of the present invention is to provide anickel-zinc ferrite possessing improved loss characteristics at highfrequencies, which ferrite also possesses a temperature coeiiicient ofinitial permeability which is markedly lower than that of previouslyknown nickel-Zinc ferrite materials.

The nature and objects of the present invention will be more fullyapparent from a consideration :of the following detailed description ofpreferred embodiments thereof, taken in connection with the accompanyingdrawings illustrating the magnetic characteristics of one embodiment ofthe nickel-zinc ferrite hereof.

In the drawings:

FIGURE l illustrates the initial permeability fr of a nickel-zincferrite as a function of the amount of tantalum pentoxide (Ta205) addedto the mixture which, when sintered, produces such ferrite;

FIGURE 2 illustrates the variation of the Q factor aS a function of thepercentage of tantalum pentoxide thus incorporated in the composition;

FIGURE 3 shows the dependence of the loss characteristics (1/,uQ) on thepercentage of tantalum pentoxide; and

FIGURE 4 shows the dependence of the temperature coefficient of initialpermeability (Ap/MEPC.) with the percentage of tantal-um pentoxide,

The objects of the present invention are achieved by providing anickel-zinc ferrite comprising a sintered mixture of from about 46 to 54mol percent ferrie oxide, from about 19 to 35 mol percent nickel oxide,from about 11 to 35 mol percent zinc oxide, and from about 0.01 to 4.6mol percent tantalum pentoxide,

It has been found that, when the indicated amounts of tantalum pentoxideare incorporated with ferrie oxide, nickel oxide and zinc oxidematerials prior to sintering, ferrites possessing materially improvedloss characteristics and temperature coeiiicients of initialpermeability result.

On the other hand, the addition of less than about 0.01 mol percenttantalum pentoxide has only a negligible effect upon the losscharacteristics of the resulting ferrite and, when tantalum pentoxide isincorporated in the mixture sintered in amounts in excess of 4.6 molpercent, we have found that the rate of decrease in the initialpermeability p is relatively large, resulting in a considerable increase(degradation) of the loss characteristics.

According to another feature :of the present invention it has beendetermined that the loss characteristics of nickel-zinc ferrites arefurther improved by incorporating amounts Vof cupric oxide and cobalticoxide, together with the tantalum pentoxide, in the material sintered to3,344,072 Patented Sept. 26, 1967 form the desired nickel-zinc ferrite.The c-upric oxide and Vcobaltic oxide adjuvants are incorporated inamounts ranging from 0.1 mol percent to 0.5 mol percent and from 0.05mol percent to 0.3 mol percent, respectively, of the materials sintered.Surprisingly, the simultaneous addition of the cupric oxide and cobalticoxide additives further improves the loss characteristics of nickel-zincferrites incorporating the same.

The nickel-zinc fer-rites hereof are manufactured by initially combiningthe several ingredients including the tantalum pentoxide, and the cupricoxide and cobaltic oxide if desired, and milling the mixture byconventional means. The mixture is thereafter heated in air by apresintering operation conducted at about 800 C. for 4 hours, compactedand molded in the conventional manner, and then subjected to a finalsinter-ing operation. The final sintering is effected in anoxygen-containing atmosphere at temperatures of from about 1030 C, to1200 C. for periods of from about 1 to 3 hours.

The following examples rare given for illustrative purposes; it will beappreciated that this invention is not restricted to the nickel-zincferrite embodiments illustrated in the examples:

Example] Varying proportions of tantalum pentoxide were admixed with acomposition constituted of 50 mol percent ferrie oxide, 22 mol percentnickel ox-ide and 28 rnol percent zinc oxide, and the resultingcompositions mixed in a revolving type steel ball mill. Each mixture wassubjected to a presintering operation in air at a temperature of S00 C.for four hours, was compacted and molded into the desired shape and wasfinally sintered in an atmosphere of pure oxygen at a temperature of1150 C. for one hour.

The values of initial permeability and of the Q factor of the severalsamples were then measured ata frequency of 3 m-c./s. at roomtemperature, and changes in the initial permeability with temperature inthe temperature range of from 0 to 40 were determined at a frequency of1 kc./s. in order to determine the values of the temperature coefficientof initial permeability.

The values determined are indicated in the following table:

TABLE I Tantalum pentoxide im Q (1/,uQ,) X106 Ait/MP C.) 10u 1n mol.percent (au-aiu) The values obtained in Table I were then plotted in thecharacteristic curves of FIGURES 1-4 of the drawing. As will be evidentfrom a consideration of FIGURE l, the initial permeability p reaches amaximum value for ferrites prepared from mixtures containing 0.05 m01percent tantalum pentoxide; for further increases in the `amount oftantalum pentoxide, the initial permeability decreases sharply at first.and then more gradually.

As Ishown in FIGURE 2 the Q factor increases rapidly with the additionof up to about 0.3 ino-l percent tantalum pentoxide, and then increasesgradually with further incremental amounts of the additive.

A comparison of the curves in FlGURES 1 and 2 readily indicates that,since the proportional increase of the value Q is much larger than the-proportional decrease of the value a, there is a marked decrease (andconsequent improvement) in the value 1/ 1Q of the loss characteristic.

Referring to FIGURE 3, the value of the loss characteristic 1/ f/.Qfalls off sharply with an increase in the amount of tantalum pentoxideuntil its concentration reaches 0.3 mol percent, has a minimum value forabout 0.8 mol percent, 'and then increases gradually with -a furtherincrease in the amount of the additive agent.

As shown in FIGURE 4, the temperature coeicient of initial permeabilityfalls of rapidly with an increase in the amount of tantalum pentoxide,4reaching a negative value when about 1.1 mol percent tantalum pentoxideis incorporated in the mixture sintered, and thereafter decreasingsteadily with further increases in the amount of tantalum pentoxide. Thevalues of the temperature coefficient of initial permeability thuschange over a Wide nange by the addition of tantalurn pentoxide invarying amount, whereby nickel-zinc ferrite samples exhibiting zero,positive, and negative temperature coeicients of initial permeabilitycan be manufactured.

Example 2 Further ferrite compositions Were prepared in the mannerdescribed in Example 1, with the exception that the final sinteringoperation was conducted in air at a tem- TABLE 1I Tantalum pentoxide imQ (1f/1Q) 10s Ait/IH" C 106 in mol. percent (ao-mm) Example 3 TABLE IIITantalum pentoxide p0 Q (1/yQ)X10 Airjli (3.))(10i in mol. percent(ao-one) It is evident from a consideration of Table III that thetantalum pentoxide effects a decrease in the temperature coefficient ofinitial permeability, irrespective of change inthe sintering conditionsemployed.

4 Example 4 Nickel-zinc ferrite samples were prepared according to themethod described in Example 1, employing mixtures of 50 mol Ipercentferrie oxide, 25 mol percent nickel oxide, 25 mol percent zinc oxide,and t-antalum pen-toxide in varying proportions. The characteristics ofthe resulting ferrites were determined :and are indicated in thefollowing table:

TABLE IV Tantalum pentoxde p0 Q, (i/l.tQ,)) 10u Ait/HP C.) X100 in mol.percent (om-140) l 287 29 120 +10. 2 290 29 119 +10. 0 164 y 75 81. 5+9.3 156 L 8O 80 +4v 3 122 8S 93. 5 +1. 3 102 99 99 2. 0 78 112 114. 54. 3

Example 5 TABLE V Tantalum pentoxide u Q, (1//.tQ) 10a Ap,ln2/ C.) 10ain mol. percent (au-a Example 6 TABLE VI Tantalum pentoxide pu Q(l/ILLQJXIOs Air/wl 0.))(10t3 in moi. percent aen-an Example 7 Theeffects of adding tantalum pentoxide to the mixture of ferrie oxide,nickel oxide and zinc oxide were maintained when the compositions offerrie oxide, nickel oxide and zinc oxides, varied from 46 mol percentto 54 mol percent, from 19 mol percent to 35 mol percent and from 11 molpercent to 35 mol percent, respectively.

Each of the samples was subjected to a sintering operacupric oxide andfrom 0.05 to 0.3 mol percent cobaltic tion in pure oxygen at 1150 C. forone hour. oxide.

The characteristics of the resulting ferrites are given 3. A method ofmanufacturing a nickel-zinc ferrite, inthe following table: comprisingTABLE V11 Composition (mol percent) Characteristic Ferrie Nickel ZineTantalum an Q (1/.LLQ)X1U@ (Apr/2P C.)X10 oxide oxide oxide pentoxideam) Example 8 Ferrite samples were manufactured from the oxidecomposition utilized in Example 4, to which was added varyingproportions of tantalum pentoxide, cupric oxide and cobaltic oxide. Thesamples were prepared employing a final sintering operation in pureoxygen at a temperature of 1150 C. for a period of one hour. Thecharacteristics of the resulting ferrite samples are given in thefollowing table:

(a) admixing from 46 to 54 mol percent ferric oxide, from 19 to 35 molpercent nickel oxide, from 11 to 35 mol percent zinc oxide, and from0.01 to 4.6 mol percent tantalum pentoxide; (b) heating the resultingmixture at 800 C. for 4 hours; (c) compacting and molding the mixtureinto the desired shape; and

(d) thereafter sintering the molded product at a tem- TABLE VIIIAdditive agents (1n mol. percent) o #o Q (1/14Q) 10 (AfL/#ZI CJXIOS(uu-M) C110 C0203 T3205 o. 5 2. 0 175 59 97 +2. 2 0. 1 173 57 101. 5+12. 9 o. 05 2. o 191 49 106. 5 2. 9 o. 1 2. 9 119 86 97. 5 0. 8 0.3 152150 50. 5 +58 0. 3 2. 0 111 114 79 0. 4

It w1ll thus be seen that the mcorporation of tantalum 55 perature offrom 1030 to 1200 C. for a perlod of pentoxide in compositions which,upon sintering, provide nickel-zinc ferrites, provides markedimprovement in the temperature coefhcients of initial permeability andin the loss characteristics of such ferrites. Since Various changes may,however, be made in the specific ferrite embodiments described abovewithout departing from the scope of the present invention, it isintended that all matter contained in the preceding description or shownin the accompanying drawings shall be interpreted as illustrative andnot in a limiting sense.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. A nickel-zinc ferrite comprising a sintered mixture of from 46 to 54mol percent fern'c oxide, from 19 to 35 mol percent nickel oxide, from11 to 35 mol percent zinc oxide, and from 0.01 to 4.6 mol percenttantalum pentoxide.

2. The nickel-zinc ferrite as defined in claim 1, in which said sinteredmixture includes from 0.1 to 0.5 mol percent from 1 to 3 hours.

4. The method as defined in claim 3, in which the mixture heated in Step(b) includes cupric oxide and cobaltic oxide in amounts of from 0.1 to0.5 mol percent and from 0.05 to 0.3 m01 percent, respectively, of saidmixture.

References Cited UNITED STATES PATENTS 2,744,873 5/ 1956 Pierkarski252-625 2,995,517 8/1961 OHara 252-625 3,062,667 11/ 1962 Pierrot et al252-625 3,062,668 11/1962 Pierrot et a1 252-625 3,208,948 9/1965 Blasse252-625 FOREIGN PATENTS 632,174 12/1961 Canada.

TOBIAS E. LEVOW, Primary Examiner. R. D. EDMONDS, Assistant Examiner.

1. A NICKEL-ZINC FERRITE COMPRISING A SINTERED MIXTURE OF FROM 46 TO 54MOL PERCENT FERRIC OXIDE, FROM 19 TO 35 MOL PERCENT NICKEL OXIDE, FROM11 TO 35 MOL PERCENT ZINC OXIDE, AND FROM 0.01 TO 4.6 MOL PERCENTTANTALUM PENTOXIDE.